1. Field of the Invention
The present invention is directed to a golf ball and, more particularly, to a golf ball having an improved dimple pattern. Still more particularly, the present invention is directed to a golf ball having a dimple pattern in which a large portion of the dimples overlap or intersect most of their neighboring dimples.
2. Description of the Related Art
Soon after the introduction of the smooth surfaced gutta percha golf ball in the mid-nineteenth century, players observed that the balls traveled further as they got older and more gouged up. The players then began to roughen the surface of new golf balls with a hammer to increase flight distance. The bramble ball, which was introduced around the turn of the twentieth century, was formed with bumps on the surface of the ball. Eventually, manufacturers began to manufacture golf balls having dimples formed in the outer surface.
The dimples on a golf ball are important in manipulating the aerodynamic forces generated by a ball in flight as a result of the ball's velocity and spin. These forces are lift and drag.
The lift force acts perpendicular to the direction of flight and is a result of air velocity differences above and below the rotating ball. Recognition of this phenomenon is attributed to Magnus and is described by Bernoulli's Equation. Bernoulli's Equation, which is a simplification of the first law of thermodynamics, relates pressure and velocity:
            p      +                        1          2                ⁢        ρ        ⁢                                  ⁢                  V          2                    +              ρ        ⁢                                  ⁢        g        ⁢                                  ⁢        h              =    c    ,where p is the pressure, ρ is the density, V is the velocity, g is the gravitational acceleration, h is elevation, and c is a constant along a streamline. We see from Bernoulli's Equation that pressure is inversely proportional to the square of velocity. With respect to the flight of a golf ball, the velocity differential—faster moving air atop the ball and slower moving air beneath the ball—results in lower air pressure above the ball and an upward directed force on the ball.
The drag force acts opposite to the direction of flight and orthogonal to the lift force. The drag force on a golf ball is attributed to parasitic drag forces, which consist of form or pressure drag and viscous or skin friction drag. A sphere is a bluff body, an inefficient aerodynamic shape. Therefore, the accelerating flow field around the golf ball will separate from its outer surface, causing a large pressure differential with high pressure forward of the ball and low pressure rearward of the ball. This pressure differential results in the majority of the drag force on the ball. In order to minimize pressure drag, dimples are provided as a means to energize the flow field with turbulence and delay the separation of flow, thus reducing the low-pressure region behind the ball. However, the turbulent boundary layer increases skin friction, which is due directly to the shear stress on the ball. The reduction in pressure drag is far greater than the increase in skin friction drag, so the net result is a large reduction in total drag.
One method of positioning or packing dimples on a golf ball divides the surface of the golf ball into eight spherical triangles corresponding to the faces of an octahedron, which is a polyhedron having eight triangular faces. Dimples are then positioned within each of the surface divisions according to a placement scheme. The surface divisions may be further divided and the resulting subdivisions packed with dimples. Octahedron-based dimple patterns generally cover approximately 60-75% of the golf ball surface with dimples. Exemplary patents disclosing octahedron-based dimple patterns include U.S. Pat. Nos. 5,415,410 and 5,957,786, the disclosures of which are incorporated herein by reference.
Another dimple packing method divides the surface of the golf ball into 20 spherical triangles corresponding to the faces of an icosahedron, which is a polyhedron having twenty triangular plane faces. Dimples are then positioned within each of the surface divisions according to a placement scheme. The surface divisions may be further divided and the resulting subdivisions packed with dimples. Because most icosahedron-based dimple patterns incorporate a high degree of hexagonal packing (that is, each dimple is surrounded by six adjacent dimples), they typically achieve more than 75% dimple coverage. Exemplary patents disclosing icosahedron-based dimple patterns include U.S. Pat. Nos. 4,560,168 and 5,957,786, the disclosures of which are incorporated herein by reference.
Some known golf ball dimple patterns have contained overlapping dimples. For example, in the dimple pattern disclosed in the family of patents including U.S. Pat. No. 4,729,861, up to 45% of the dimple spacings may overlap. However, the design teaches to minimize the distance of overlap such that the overlap is no greater than about 0.02 inches. With the type of dimple pattern disclosed, it is typical that most overlaps will involve a maximum of only two neighboring dimples.
Another dimple pattern is disclosed in the family of patents including U.S. Pat. No. 4,877,252. In this dimple pattern, at least 10% of the dimples have overlap. However, the overlapping dimples overlap relatively few of their neighboring dimples, resulting in a low overlap saturation as that term is defined and used below.
These and other dimples patterns, of course, may be adjusted to accommodate a parting line, or for other reasons.
Another dimple pattern is disclosed in the family of patents including U.S. Pat. No. 5,273,287. In this dimple pattern, some of the dimples overlap in order to obtain a “substantial surface coverage” of dimples using one dimple size. However, overlap is undesired and is therefore kept to “some small percentage.”
Another dimple pattern is disclosed in the family of patents including U.S. Pat. No. 5,356,150. In this dimple pattern, the dimples are elongated and have some amount of overlap. A similar dimple pattern to the same assignee is disclosed in the family of patents including U.S. Pat. No. 6,206,792. This dimple pattern also contains elongated dimples, but overlap is discouraged.
Another dimple pattern is disclosed in the family of patents including U.S. Pat. No. 5,688,194. This dimple pattern is generated automatically, starting with a random, overlapping layout of dimples. The dimple positions are then adjusted to avoid overlap.
Another dimple pattern is disclosed in the family of patents including U.S. Pat. No. 5,842,937. In this dimple pattern, dimple locations are defined using fractal geometry. Dimple overlap is contemplated, but no specifics are provided.